This invention relates to a method of drawing fibers, yarns, or relatively narrow plastic tapes and to apparatus for use in carrying out the method and more particularly to the drawing of synthetic fibers, yarns or narrow tapes. In the description of this invention which follows, for the sake of convenience, the method and apparatus will be described in terms of drawing fibers. However, it is to be understood that the method and apparatus are equally usable for drawing any elongated body subject to such procedure.
The term drawing is used herein with reference to the elongation of a fiber by between 200% and 2000% in a manner that increases the orientation of the fiber molecules in the longitudinal direction. The term should be distinguished from a lesser elongation, which is generally characterized as stretching.
In the production of most synthetic fibers and particularly those which are melt spun, such as nylon and polyester fibers, a drawing stage must be included subsequent to the spinning or extrusion stage in which the fibers are drawn or physically elongated to several times their original length. The drawing of the fibers is to enable them to achieve the required molecular orientation and structure by virtue of which they attain the necessary strength and other desired physical characteristics. This drawing has generally been hitherto effected on a commercial scale by passing the fiber from one to another set of rotating rollers, each set of rollers rotating at a surface speed which is greater than that of the preceding set. The ratio of the higher to the lower surface speeds determines the extent of fiber drawing. This ratio is called the "draw ratio" and a typical draw ratio for nylon fibers is about 4.8 to 1. With such conventional and known draw methods the fiber is subjected to a very abrupt acceleration and rise in tension at the point where it leaves one roller to pass to the succeeding higher speed roller and care must be taken to ensure that the abrupt rise in tension does not result in the breaking of the fiber. Thus with this conventional technique, which may be termed "inpulse drawing" because the fiber experiences a sudden inpulsive acceleration from its initial undrawn rate of travel through the draw machine to its final drawn rate of travel through the draw machine, an upper limit of draw speed exists beyond which danger of fiber breakage occurs because of the high fiber tensions that are imposed on the yarn during its "impulsive" acceleration. Furthermore, the drawing process must be carried out at surface speeds which are considerably less than the speed of fiber production by extrusion of melt spinning and in consequence the drawing stage may well be some twenty to 100 times slower than the extrusion or melt spinning stage. Therefore, the drawing of fibers constitutes a major factor in the slowing down of fiber production and contributes to production expense. Exemplary of method and apparatus designed to achieve all or at least a part of fiber elongation through such "impulse drawing" are described in U.S. Pat. Nos. 3,551,550 and 2,372,627. It would therefore be desirable to have an improved method and apparatus for drawing fibers, yarns, tapes and similar configurations formed from synthetic resins.
It is a primary object of this invention to provide improved method and apparatus for drawing fibers, monofilaments, etc., the method and apparatus giving rise to drawn fibers having improved physical characteristics, in particular tensile strength. It is another object of this invention to provide method and apparatus of the character described which may effect such drawing at a speed equivalent to that at which the fibers are melt spun or extruded, thus making an intermediate storage of the fibers unnecessary. It is yet another object of this invention to provide method and apparatus of the character described which provide for the ready attainment of variable draw ratios, whether continuous or discontinuous, which make possible the periodic variation in physical characteristics along the length of the fibers and which make possible the incorporation of other physical and chemical treatments at various points during the gradual drawing process. It is yet a further object of this invention to provide method and apparatus of the character described which make possible the gradual acceleration of moving fibers between undrawn and drawn speeds so as to reduce both the fibers tension and the power required to accelerate fibers during drawing.
Another object of this invention is to provide a method and apparatus for preparing textured fibers having high crimp retentivity and high retractive force. A further object is to provide a method and apparatus for drawing monofilaments with improved cross-sectional uniformity and also without causing cross-sectional distortion or asymmetry. Other objects of the invention will in part be obvious and will in part be apparent hereinafter.
The invention accordingly comprises the several steps and the relation of one or more of such steps with respect to each of the others, and the apparatus embodying features of construction, combinations of elements and arrangement of parts which are adapted to effect such steps, all as exemplified in the following detailed disclosure, and the scope of the invention will be indicated in the claims.